A fiber reinforced thermoplastic resin (FRTP) is light and excellent in strength, and thus often used in an exterior of a vehicle, a vessel, and the like. Among the fiber reinforced thermoplastic resin, particularly a long fiber reinforced thermoplastic resin (LFRTP) containing reinforced fibers whose fiber length is long is excellent in shock resistance and rigidity, and thus frequently used in a bumper and a body of an automobile in recent years.
A molded article of such a long fiber reinforced thermoplastic resin is produced from a resin material formed by melting pellets, and the reinforced fibers whose fiber length is long are dispersed and distributed in the pellets. For example, Patent Document 1 discloses a method for producing pellets, including pultruding a plurality of reinforced fiber bundles such as glass rovings impregnated in a molten thermoplastic resin bath from the thermoplastic resin bath while twisting the reinforced fiber bundles to form a strand in which reinforced fibers are coated with a thermoplastic resin, and cutting the strand to a predetermined length to obtain the pellets.
In this method for producing the pellets, a pair of take-up rolls is arranged on the downstream side of the thermoplastic resin bath, and these rolls are arranged so as to be inclined in the directions different from each other with respect to the pultruding direction of the strand. Therefore, in the method for producing the pellets of Patent Document 1, by nipping the reinforced fiber bundles between these rolls, the strand in which the reinforced fiber bundles are twisted is produced as an intermediate body.
In the strand serving as the intermediate body pultruded in such a way, the reinforced fiber bundles are firmly tightened to each other due to twisting, and the reinforced fiber bundles are gathered on the center side of the strand. The reinforced fibers on the center side are coated with the thermoplastic resin so as to be surrounded. Therefore, when the strand is pultruded from a die, the thermoplastic resin plays a role of lubrication and helps pultruding of the strand, and the reinforced fibers are not brought into contact with the die and do not serve as resistance against the pultruding of the strand. As a result, the strand can be pultruded with smaller force than a conventional method for producing in which reinforced fiber bundles are pultruded in parallel. Since the resistance against the pultruding of the strand is small, there is an advantage that production speed of the pellets can be increased.
In the method of producing of Patent Document 1 in which production is performed with twisting, the reinforced fiber bundles are tightened due to the twisting, so that a volume thereof is reduced. Thus, there is also an advantage that a contained amount of the reinforced fibers can be easily increased, and hence a content rate of the reinforced fibers can be increased in comparison to the conventional method for producing in which the reinforced fibers are pultruded in parallel.